Treatment progress tracking and recalibration

ABSTRACT

The present invention relates to systems and methods of developing and tracking delivery and patient progression through an orthodontic treatment plan. One method includes identifying deviations from an orthodontic treatment plan, including receiving a digital representation of an actual arrangement of a patient&#39;s teeth after an orthodontic treatment plan has begun for the patient and prior to completion of the orthodontic treatment plan. The method further includes comparing the actual arrangement to a pre-determined planned arrangement to determine if the actual arrangement substantially deviates from the planned arrangement, the comparing comprising matching teeth from a previously segmented model to a surface of an unsegmented representation of the actual arrangement; and calculating one or more positional differences between the actual and planned arrangements of at least some of the corresponding teeth.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/341,645, filed Jul. 25, 2014, which is a continuation of U.S. patentapplication Ser. No. 14/034,373, filed Sep. 23, 2013, now U.S. Pat. No.8,899,978, issued Dec. 2, 2014, which is a continuation of U.S. patentapplication Ser. No. 11/760,705, filed Jun. 8, 2007, now U.S. Pat. No.8,562,338, issued Oct. 22, 2013, the entire contents of each of whichare incorporated herein by reference.

This application is related to U.S. patent application Ser. No.11/460,689, filed Jun. 8, 2007; U.S. patent application Ser. No.11/760,701, filed Jun. 8, 2007; and U.S. patent application Ser. No.11/760,612, filed Jun. 8, 2007, now U.S. Pat. No. 8,075,306, issued Dec.13, 2011; the contents of each of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of orthodontics,and more particularly to systems and methods of developing and trackingdelivery and patient progression through an orthodontic treatment plan.

An objective of orthodontics is to move a patient's teeth to positionswhere function and/or aesthetics are optimized. Traditionally,appliances such as braces are applied to the patient's teeth by anorthodontist or dentist and the set of braces exerts continual force onthe teeth and gradually urges them toward their intended positions. Overtime and with a series of clinical visits and adjustments to the braces,the orthodontist adjusts the appliances to move the teeth toward theirfinal destination.

More recently, alternatives to conventional orthodontic treatment withtraditional affixed appliances (e.g., braces) have become available. Forexample, systems including a series of preformed aligners have becomecommercially available from Align Technology, Inc., Santa Clara, Calif.,under the tradename Invisalign® System. The Invisalign® System includesdesigning and/or fabricating multiple, and sometimes all, of thealigners to be worn by the patient before the aligners are administeredto the patient and used to reposition the teeth (e.g., at the outset oftreatment). Often, designing and planning a customized treatment for apatient makes use of computer-based 3-dimensional planning/design tools,such as ClinCheck® from Align Technology, Inc. The design of thealigners can rely on computer modeling of a series of planned successivetooth arrangements, and the individual aligners are designed to be wornover the teeth and elastically reposition the teeth to each of theplanned tooth arrangements.

While patient treatment and tooth movements can be plannedprospectively, in some cases orthodontic treatment can deviate from theplanned treatment or stages. Deviations can arise for numerous reasons,and can include biological variations, poor patient compliance, and/orfactors related to biomechanical design. In the case of aligners,continued treatment with previously designed and/or fabricated alignerscan be difficult or impossible where a patient's teeth deviatesubstantially from the planned treatment course. For example, subsequentaligners may no longer fit the patient's teeth once treatmentprogression has deviated from the planned course. Because detecting adeviation from planned treatment most typically relies on visualinspection of the patient's teeth or observation of appliances no longerfitting, treatment can sometimes progress significantly off track by thetime a deviation is detected, thereby making any required correctivemeasures more difficult and/or substantial. Earlier and better off trackdeterminations would, therefore, be beneficial in order to recalibratethe fit of the aligner device on the teeth. Accordingly, improvedmethods and techniques of detecting and correcting treatment that hasdeviated from planned or desired treatment course would be desirable,particularly methods allowing early detection of treatment deviation.

SUMMARY OF THE INVENTION

The present invention provides improved systems and methods for trackinga patient's progress according to a planned treatment, incorporatingenhanced tracking techniques into treatment delivery and management,and, if necessary, revising or modifying the patient's treatment planbased on a determination that treatment has progressed off track.Information obtained according to the invention techniques can be used,for example, to more actively and/or effectively manage delivery oforthodontic treatment, increasing treatment efficacy and successfulprogression to the patient's teeth to the desired finished positions.

Thus, in one aspect, the present invention includes systems and methodsof identifying deviations from an orthodontic treatment plan. A methodcan include, for example, receiving a digital representation of anactual arrangement of a patient's teeth after an orthodontic treatmentplan has begun for the patient and prior to completion of theorthodontic treatment plan; and comparing the actual arrangement to apre-determined planned arrangement to determine if the actualarrangement substantially deviates from the planned arrangement, andcalculating one or more positional differences between the actual andplanned arrangements of at least some of the corresponding teeth.

The present invention further includes systems and methods of managingdelivery and patient progression through an orthodontic treatment plan.Such a method can include, for example, providing an initial treatmentplan for a patient, providing a set of orthodontic appliances, trackingprogression of the patient's teeth along the treatment path, comparingthe actual arrangement with a planned arrangement to determine if theactual arrangement of the teeth matches a planned tooth arrangement, andgenerating a revised treatment plan where it is determined that theactual tooth arrangement deviates from the planned tooth arrangement. Inanother example, a method can include receiving a digital representationof an actual arrangement of a patient's teeth after an orthodontictreatment plan has begun for the patient and prior to completion of theorthodontic treatment plan; comparing the actual arrangement to adigital model of a planned arrangement, and generating a revisedtreatment plan.

A system can include a computer coupled to a server, the computercomprising a processor and a computer readable medium comprisinginstructions which, if executed, cause the computer to: receive adigital representation of an actual arrangement of a patient's teethafter the orthodontic treatment plan has begun for the patient and priorto completion of the orthodontic treatment plan; compare the actualarrangement to a pre-determined planned arrangement; and calculate oneor more positional differences between the actual and plannedarrangements of at least some of the corresponding teeth; and generate arevised treatment plan.

A system according to another embodiment of the present invention caninclude a computer coupled to a server, the computer comprising aprocessor and a computer readable medium comprising instructions which,if executed, cause the computer to generate an initial treatment planfor a patient including enhanced tracking of the patient's treatmentprogress, provide a set of orthodontic appliances corresponding to atreatment phase, track progression of the patient's teeth along atreatment path, compare the actual arrangement with a plannedarrangement, and generate a revised treatment plan where it isdetermined that the actual tooth arrangement substantially deviates fromthe planned tooth arrangement.

For a fuller understanding of the nature and advantages of the presentinvention, reference should be made to the ensuing detailed descriptionand accompanying drawings. Other aspects, objects and advantages of theinvention will be apparent from the drawings and detailed descriptionthat follows.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 is a diagram showing the anatomical relationship of the jaws of apatient.

FIG. 2A illustrates in more detail the patient's lower jaw and providesa general indication of how teeth may be moved according to anembodiment of the present invention.

FIG. 2B illustrates a single tooth from FIG. 2A and definesdetermination of tooth movement distance according to an embodiment ofthe present invention.

FIG. 2C illustrates the jaw of FIG. 2A together with an incrementalpositioning adjustment appliance according to an embodiment of thepresent invention.

FIG. 3 shows generating and administering treatment according to anembodiment of the present invention.

FIG. 4 illustrates generating a treatment plan according to anembodiment of the present invention.

FIG. 5 illustrates a process including teeth matching according to oneembodiment of the present invention.

FIG. 6 shows a process including teeth matching according to anotherembodiment of the present invention.

FIG. 7 is a screen shot showing a graphical representation of athree-dimensional model of a patient's upper and lower jaws based on acurrent digital data set representing teeth in their current positions,according to an embodiment of the present invention.

FIG. 8 is a graphical representation of a three-dimensional model of aninitial match that can occur when the three dimensional model of digitaltranslated images are overlaid on three dimensional model of the CurrentTeeth Image, according to one embodiment of the present invention.

FIG. 9A through FIG. 9C show plurality of stages of teeth correction andrevision of treatment, according to several embodiments of the presentinvention.

FIG. 10 is a block diagram illustrating a system for generatingappliances in accordance with methods and processes of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The invention described herein provides improved systems and methods fortracking a patient's progress according to a planned treatment,incorporating enhanced tracking techniques into treatment delivery andmanagement, and, if necessary, revising or modifying the patient'streatment plan based on a determination that treatment has progressedoff track. Systems and methods of treatment progress tracking andrevised planning can be included in a variety of orthodontic treatmentregimens. For example, the progress tracking and revised planningfeatures can be optionally included and incorporated into other aspectsof treatment according to the Invisalign® System. Treatment can bepre-planned for administering to a patient in a series of one or morephases, with each phase including a set of appliances that are wornsuccessively by the patient to reposition the teeth through plannedarrangements and eventually toward a selected final arrangement.Progress tracking, according to the present invention, is incorporatedinto the pre-planned treatment for monitoring and management, and toprovide enhanced detection and feedback as to whether treatment isprogressing on track.

Tracking can occur at any point during treatment but will typically bescheduled to correspond with a patient completing a pre-planned phase oftreatment (e.g., wearing each appliance in a designated set). Forexample, once initial staging of a patients teeth is completed (e.g.,model initial, intermediate, and final teeth arrangements) and atreatment plan has been devised, a dental practitioner can be sent afirst set of one or more appliances to be administered to the patient inthe first phase of treatment. After the last appliance in the first setis administered to the patient, an image of the patient's teeth in theirpositions following administration of the first set of appliances can betaken (e.g., scan, impression, etc.). From the image of the patient'steeth in their current position, an assessment is made as to how thetreatment is tracking relative to the original treatment projections. Ifthere is a substantial deviation from the planned treatment path, thencorrective action can be taken, for example, in order to achieve theoriginal designed final position. Treatment then progresses to the nextphase, where treatment is either finalized if the intended finalpositions are reached, or a second set of appliances can be sent to thepractitioner for administration to the patient. The second set ofappliances can be based on the initial treatment plan if treatment isprogressing on track, or can be based on a revised or modified treatmentplan where a determination is made that treatment is off track.

Methods and techniques for tracking and preserving the original finalposition in the treatment is generally referred to herein as “teethmatching” or “bite matching”. For example, bite matching techniquesdescribed herein can include matching teeth from the original image ofthe teeth or impression, to surface(s) of a new model of the teeth takenafter treatment has begun. An off-track determination can be followed by“re-setting” to the actual position of the teeth as defined by datarepresented in the progress scan, the original data of the teeth (i.e.,segmented models from initial treatment plan), thereby allowingpreservation of the initially selected final target position of theteeth. In other words, the original data set which contains with it, anestablished target arrangement, can be reused, by repositioning theteeth arrangement according to the positions of the (same) teethcaptured in the progress scan. In so doing, a new planned path to gofrom the current to the target can be recreated without having to changethe original target configuration. This method is enabled by using bitematching techniques to allow the current aligner geometry to berecalibrated and reshaped according to the actual position of the teethin the progress scan. Using such bite matching techniques providessignificant advantages in terms of efficiency as there is no need tore-segment and process the new scan of the teeth, and in terms ofefficacy since the initial final arrangement is preserved, even if thepatient progresses off track.

Incorporating the inventive techniques and tracking methods describedherein in managing delivery/modification would provide variousadvantages, including earlier detection of treatment deviations,allowing earlier remedial measures to be taken, if necessary, to avoidundesirable treatment outcomes and preservation of initial treatmentgoals, thereby ultimately allowing for more effective treatment andbetter clinical outcomes. Furthermore, treatment efficiency and efficacycan be increased by better avoidance of inefficient/undesirabletreatment “detours”. Additionally, improved monitoring and tracking, asdescribed, is more objective and reliable, and less qualitative innature than the common practice of visually identifying off-trackprogress. This reduces the inter-clinician variability and reduces thedependency of accurate detection on clinician experience. As such,currently described inventive methods and techniques can inspire moreconfidence in both patients and practitioners, including practitionersthat may be less experienced with a given treatment method and/or lessconfident in their abilities to clinically detect off-track progression,or even more experienced practitioners who desire more detailedmonitoring, for example, in cases involving more difficult or lesspredictable movements.

FIG. 1 shows a skull 10 with an upperjaw bone 22 and a lowerjaw bone 20.The lowerjaw bone 20 hinges at a joint 30 to the skull 10. The joint 30is called a temporal mandibular joint (TMJ). The upperjaw bone 22 isassociated with an upper jaw 101, while the lower jaw bone 20 isassociated with a lower jaw 100. A computer model of the jaws 100 and101 is generated, and a computer simulation models interactions amongthe teeth on the jaws 100 and 101. The computer simulation allows thesystem to focus on motions involving contacts between teeth mounted onthe jaws. The computer simulation allows the system to render realisticjaw movements that are physically correct when the jaws 100 and 101contact each other. The model of the jaw places the individual teeth ina treated position. Further, the model can be used to simulate jawmovements including protrusive motions, lateral motions, and “toothguided” motions where the path of the lower jaw 100 is guided by teethcontacts rather than by anatomical limits of the jaws 100 and 101.Motions are applied to one jaw, but may also be applied to both jaws.Based on the occlusion determination, the final position of the teethcan be ascertained.

Referring now to FIG. 2A, the lower jaw 100 includes a plurality ofteeth 102, for example, At least some of these teeth may be moved froman initial tooth arrangement to a final tooth arrangement. As a frame ofreference describing how a tooth may be moved, an arbitrary centerline(CL) may be drawn through the tooth 102. With reference to thiscenterline (CL), each tooth may-be moved in orthogonal directionsrepresented by axes 104, 106, and 108 (where 104 is the centerline). Thecenterline may be rotated about the axis 108 (root angulation) and theaxis 104 (torque) as indicated by arrows 110 and 112, respectively.Additionally, the tooth may be rotated about the centerline, asrepresented by an arrow 112. Thus, all possible free-form motions of thetooth can be performed.

FIG. 2B shows how the magnitude of any tooth movement may be defined interms of a maximum linear translation of any point P on a tooth 102.Each point P1 will undergo a cumulative translation as that tooth ismoved in any of the orthogonal or rotational directions defined in FIG.2A. That is, while the point will usually follow a nonlinear path, thereis a linear distance between any point in the tooth when determined atany two times during the treatment. Thus, an arbitrary point P1 may infact undergo a true side-to-side translation as indicated by arrow d1,while a second arbitration point P2 may travel along an accurate path,resulting in a final translation d2. Many aspects of the presentinvention are defined in terms of the maximum permissible movement of apoint P1 induced on any particular tooth. Such maximum tooth movement,in turn, is defined as the maximum linear translation of that point P1on the tooth that undergoes the maximum movement for that tooth in anytreatment step.

FIG. 2C shows one adjustment appliance 111 which is worn by the patientin order to achieve an incremental repositioning of individual teeth inthe jaw as described generally above. The appliance can include a shell(e.g., polymeric shell) having teeth-receiving cavities that receive andresiliently reposition the teeth. Such appliances, including thoseutilized in the Invisalign® System, are described in numerous patentsand patent applications assigned to Align Technology, Inc. including,for example in U.S. Pat. Nos. 6,450,807, and 5,975,893, as well as onthe company's website, which is accessible on the World Wide Web (see,e.g., the url “align.com”).

As set forth in the prior applications, each appliance may be configuredso that its tooth-receiving cavity has a geometry corresponding to anintermediate or final tooth arrangement intended for the appliance. Thepatient's teeth are progressively repositioned from their initial tootharrangement to a final tooth arrangement by placing a series ofincremental position adjustment appliances over the patient's teeth. Theadjustment appliances can be generated all at the same stage or in setsor batches, e.g., at the beginning of a stage of the treatment, and thepatient wears each appliance until the pressure of each appliance on theteeth can no longer be felt or has resulted in the maximum allowabletooth movement for that given stage. A plurality of different appliances(e.g., set) can be designed and even fabricated prior to the patientwearing any appliance of the plurality. At that point, the patientreplaces the current appliance with the next appliance in the seriesuntil no more appliances remain. The appliances are generally notaffixed to the teeth and the patient may place and replace theappliances at any time during the procedure. The final appliance orseveral appliances in the series may have a geometry or geometriesselected to overcorrect the tooth arrangement, i.e., have a geometrywhich would (if fully achieved) move individual teeth beyond the tootharrangement which has been selected as the “final.” Such over-correctionmay be desirable in order to offset potential relapse after therepositioning method has been terminated, i.e., to permit movement ofindividual teeth back toward their pre-corrected positions.Over-correction may also be beneficial to speed the rate of correction,i.e., by having an appliance with a geometry that is positioned beyond adesired intermediate or final position, the individual teeth will beshifted toward the position at a greater rate. In such cases, the use ofan appliance can be terminated before the teeth reach the positionsdefined by the appliance.

Referring to FIG. 3, a method 200 according to the present invention isillustrated. Individual aspects of the process are discussed in furtherdetail below. The process includes generating a treatment plan forrepositioning a patient's teeth (Step 202). Briefly, a treatment planwill include obtaining data comprising an initial arrangement of thepatient's teeth, which typically includes obtaining an impression orscan of the patient's teeth prior to the onset of treatment. Thetreatment plan will also include identifying a final or targetarrangement of the patient's teeth that is desired, as well as aplurality of planned successive or intermediary tooth arrangements formoving the teeth along a treatment path from the initial arrangementtoward the selected final or target arrangement. Appliances can begenerated based on the planned arrangements and administered to thepatient (Step 204). The appliances are typically administered in sets orbatches of appliances, such as sets of 2, 3, 4, 5, 6, 7, 8, 9, or moreappliances, but are not limited to any particular administrative scheme.After the treatment plan begins and following administration ofappliances to the patient, teeth matching is done to assess a currentand actual arrangement of the patient's teeth compared to a plannedarrangement (Step 206). If the patient's teeth are determined to be“on-track” and progressing according to the treatment plan, thentreatment progresses as planned. If the patient's teeth have reached theinitially planned final arrangement, then treatment progresses to thefinal stages of treatment (Step 208). Where the patient's teeth aredetermined to be tracking according to the treatment plan, but have notyet reached the final arrangement, the next set of appliances can beadministered to the patient (repeat Step 204, according to the initialTreatment Plan). If, on the other hand, the patient's teeth aredetermined at the teeth matching step (Step 206) not to be tracking withthe treatment plan, then treatment is characterized as “off-track” andan assessment is made as to how further treatment of the patient willproceed. Typically, a revised treatment plan will be generated (Step210), and may be selected, for example, to reposition the teeth from thecurrent position to a final position, which may be the same destinationas the initially determined final position according to the initialtreatment plan.

Systems of the present invention can include network based systems,including a data network and a server terminal operatively coupled tothe network. One or more client terminals can be included andoperatively coupled to the network. Systems can optionally include morestand-alone or non-network based systems, including computers andsoftware packages designed to at least partially operate independent ofa data network and in which various steps of the currently describedmethods can be accomplished in an automated fashion at a remote location(e.g., practitioner's office).

FIG. 4 illustrates the general flow of an exemplary process 300 fordefining and generating a treatment plan, including repositioningappliances for orthodontic treatment of a patient. The process 300includes the methods, and is suitable for the apparatus, of the presentinvention, as will be described. The steps of the process can beimplemented as computer program modules for execution on one or morecomputer systems.

As an initial step, a mold or a scan of patient's teeth or mouth tissueis acquired (Step 302). This generally involves taking casts of thepatient's teeth and gums, and may in addition or alternately involvetaking wax bites, direct contact scanning, x-ray imaging, tomographicimaging, sonographic imaging, and other techniques for obtaininginformation about the position and structure of the teeth, jaws, gumsand other orthodontically relevant tissue. From the data so obtained, adigital data set is derived that represents an initial (e.g.,pretreatment) arrangement of the patient's teeth and other tissues.

The initial digital data set, which may include both raw data fromscanning operations and data representing surface models derived fromthe raw data, is processed to segment the tissue constituents from eachother (Step 304), including defining discrete dental objects. Forexample, data structures that digitally represent individual toothcrowns can be produced. In some embodiments, digital models of entireteeth are produced, including measured or extrapolated hidden surfacesand root structures.

Desired final position of the teeth, or tooth positions that are desiredand/or intended end result of orthodontic treatment, can be received,e.g., from a clinician in the form of a descriptive prescription, can becalculated using basic orthodontic prescriptions, or can be extrapolatedcomputationally from a clinical prescription (Step 306). With aspecification of the desired final positions of the teeth and a digitalrepresentation of the teeth themselves, the final position and surfacegeometry of each tooth can be specified (Step 308) to form a completemodel of the teeth at the desired end of treatment. The result of thisstep is a set of digital data structures that represents a desiredand/or orthodontically correct repositioning of the modeled teethrelative to presumed-stable tissue. The teeth and surrounding tissue areboth represented as digital data.

Having both a beginning position and a final target position for eachtooth, the process next defines a treatment path or tooth path for themotion of each tooth (Step 310). This includes defining a plurality ofplanned successive tooth arrangements for moving teeth along a treatmentpath from an initial arrangement to a selected final arrangement. In oneembodiment, the tooth paths are optimized in the aggregate so that theteeth are moved in the most efficient and clinically acceptable fashionto bring the teeth from their initial positions to their desired finalpositions.

At various stages of the process, the process can include interactionwith a clinician responsible for the treatment of the patient (Step312). Clinician interaction can be implemented using a client processprogrammed to receive tooth positions and models, as well as pathinformation from a server computer or process in which other steps ofprocess 300 are implemented. The client process is advantageouslyprogrammed to allow the clinician to display an animation of thepositions and paths and to allow the clinician to reset the finalpositions of one or more of the teeth and to specify constraints to beapplied to the segmented paths.

The tooth paths and associated tooth position data are used to calculateclinically acceptable appliance configurations (or successive changes inappliance configuration) that will move the teeth on the definedtreatment path in the steps specified (Step 314). Each applianceconfiguration corresponds to a planned successive arrangement of theteeth, and represents a step along the treatment path for the patient.The steps are defined and calculated so that each discrete position canfollow by straight-line tooth movement or simple rotation from the toothpositions achieved by the preceding discrete step and so that the amountof repositioning required at each step involves an orthodonticallyoptimal amount of force on the patient's dentition. As with other steps,this calculation step can include interactions with the clinician (Step312).

Having calculated appliance definitions, the process 300 can proceed tothe manufacturing step (Step 316) in which appliances defined by theprocess are manufactured, or electronic or printed information isproduced that can be used by a manual or automated process to defineappliance configurations or changes to appliance configurations.Appliances according to the treatment plan can be produced in entirety,such that each of the appliances are manufactured (e.g., prior totreatment), or can be manufactured in sets or batches. For example, insome cases in might be appropriate to manufacture an initial set ofappliances at the outset of treatment with the intention ofmanufacturing additional sets of appliances (e.g., second, third,fourth, etc.) after treatment has begun (e.g., as discussed furtherherein). For example, a first set of appliances can be manufactured andadministered to a patient. Following administration, it may be desirableto track the progression of the patient's teeth along the treatment pathbefore manufacturing and/or administering subsequent set(s) ofappliances.

Generating and/or analyzing digital treatment plans, as discussedherein, can include, for example, use of 3-dimensional orthodontictreatment planning tools such as ClinCheck from Align Technology, Inc.or other software available from eModels and OrthoCAD, among others.These technologies allow the clinician to use the actual patient'sdentition as a starting point for customizing the treatment plan. TheClinCheck technology uses a patient-specific digital model to plot atreatment plan, and then uses a processed (e.g., segmented) scan of theachieved treatment outcome to assess the degree of success of theoutcome as compared to the original digital treatment plan as, asdiscussed in U.S. Pat. Nos. 7,156,661 and 7,077,647 (see also, below).

In some cases, patients do not progress through treatment as expectedand/or planned. For example, in some instances a patient's progressionalong a treatment path can become “off-track” or will deviate from aninitial treatment plan, whereby an actual tooth arrangement achieved bythe patient will differ from the expected or planned tooth arrangement,such as a planned tooth arrangement corresponding to the shape of aparticular appliance. A determination that the progression of apatient's teeth is deviating or not tracking with the original treatmentplan can be accomplished in a variety of ways. As set forth above,off-track deviations can be detected by visual and/or clinicalinspection of the patient's teeth. For example, a substantial off trackdeviation from the expected or planned treatment may become apparentwhen the patient tries to wear a next appliance in a series. If theactual tooth arrangement substantially differs from the plannedarrangement of the teeth, the next appliance will typically not be ableto seat properly over the patient's teeth. Thus, an off-track deviationmay become substantially visually apparent to a treating professional,or even to the patient, upon visual or clinical inspection of the teeth.

Detecting deviations from a planned treatment, however, can bedifficult, particularly for patients as well as certain dentalpractitioners, such as those with more limited experience inorthodontics, certain general dentist, technicians and the like.Additionally, deviations that have progressed to the point that they arevisually detectable clinically are often substantially off track withrespect to the planned treatment, and earlier means of off-trackdetection is often desired. Thus, detecting deviations from a treatmentplan can also be accomplished by comparing digital models of thepatients teeth, and can often detect deviations from a treatment planbefore the deviation becomes substantially apparent by visual orclinical inspection.

An exemplary computer based teeth matching process according to anembodiment of the present invention is described with reference to FIG.5. First, data from an earlier treatment plan is received (Step 402).Typically, data includes the initial data set or image data representingthe patient's teeth in the original, pre-treatment positions, theinitially identified final position, as well as planned intermediate orsuccessive arrangements selected for moving teeth along the initialtreatment path from the initial arrangement to the selected finalarrangement. Next, a current jaw impression or data including a digitalrepresentation of the teeth in their current positions, after treatmenthas begun, is received and loaded (Step 404). Data including plannedarrangements of the teeth are then compared to data including arepresentation of the patient's teeth in their current positions for aninitial determination of whether a match exists (Step 406). Next, thenew jaw data is segmented and positioned in the original coordinatesystem (Step 408). The process then compares the original jaw dataagainst the new jaw data (Step 410). Based on the comparison, theprocess generates an analysis report (Step 412), new/revised treatmentoptions or plans (Step 414), and/or allows visualization of any detecteddiscrepancy (Step 416). See also, e.g., U.S. Pat. Nos. 7,156,661 and7,077,647, for discussion of comparing actual position of the teethrelative to a planned or expected position using a processed (e.g.,segmented) scan of the teeth positions following initiation oftreatment.

In some instances, detecting a deviation from a treatment plan viacomparison between digital models of the patients teeth can includecomparing a current scan or image, which has not been segmented, of thepatients teeth in a position after treatment has begun to a previouslysegmented data set of the patients teeth at a current, past or futurestage. Use of an unsegmented, rather than segmented, digitalrepresentation of the current teeth positions may be desirable, forexample, in order to avoid resource and/or labor intensive processingsteps to transform the current unsegmented digital teeth model to asegmented digital teeth model. In addition, lower resolution or qualityscans or images can save cost and time if the necessary reference pointscan be identified on the unsegmented current scan or image.

FIG. 6 is a flow chart showing the steps of correcting deviations from aplanned course of treatment to gradually reposition teeth, according toone embodiment of the present disclosure. The process starts in step600, when current jaw data or “Current Teeth Image” is received. Thecurrent jaw data includes data representing an actual arrangement of thepatients teeth following administration of appliances according to theoriginal treatment plan. In step 602, the Current Teeth Image ispre-processed using a digital data tool (DDT) such that each tooth isassigned a Facial Axis of the Clinical Crown (FACC), i.e. a uniquecurrent identifier, with jaw characteristics set. Typically, accordingto the described embodiment, the Current Teeth Image does not need to besegmented, which saves a technician's time and hence overall cost.

In step 604, a Previously Segmented Teeth Model is selected, and isinput into a system of the present invention for analysis and comparisonwith the Current Teeth Image. The Previously Segmented Teeth Modelselected can include an Initially Segmented Teeth Model or a digitalmodel of the patient's teeth in their initial, pre-treatment positions,the initial final position according to the initial or previoustreatment plan (e.g., Prescribed Tooth Arrangement), or a plannedsuccessive tooth arrangement therebetween.

In step 606, the Previously Segmented Teeth Model and the Current TeethImage are compared. This step includes a sort of “rough match” of thesegmented model and the Current Teeth Image to identify correspondingfeatures of the two models that may be compared (Step 608). For example,an initial matching algorithm can be executed which matches uniquestarting identifiers (FACCs) of each tooth in the Previously SegmentedTeeth Model to the respective unique current identifiers (FACCs) of eachtooth in the Current Teeth Image. The images can be overlaid on eachother and the relative location of each tooth identified by its uniqueidentifier (or FACC) to determine if there are any mismatches in step608.

If any mismatches are found, an initial match has not occurred and themismatches are displayed in the form of an informational dialog thatprovides details of the mismatches, such as teeth numberingirregularities or missing FACCs. A mismatch can occur, for example, ifthere are any teeth numbering irregularities, such as the total numberof teeth in each model is not the same, or at least one tooth is missinga FACC. Mismatches may result, for example, where substantial dentalwork or reconstruction (e.g., tooth extraction, tooth reconstruction,filling, etc.) has occurred following the initial treatment plan orgeneration of Previously Segmented Teeth Model.

In Step 610, initial mismatch errors as identified above can be manuallyaccounted for in the process. For example, a technician can manuallyadjust or reposition each tooth with a mismatch using the PreviouslySegmented Teeth Model or adjusts the information relating to each toothwith a mismatch (e.g., accounting for an extracted tooth).

If no mismatches are generated in step 608, or where mismatches havebeen accounted for according to 610, then an initial match occurs andthe process moves to step 612. The initial match confirms that thetechnician is using the correct Previously Segmented Teeth Model and theCurrent Teeth Image, which provides a good starting point for executinga surface matching algorithm.

In step 612, more detailed matching and comparison between PreviouslySegmented Teeth Model and the Current Teeth Image occurs, which includesexecution a surface matching algorithm. The surface matching algorithmcan take a number of samples of each tooth in the Previously SegmentedTeeth Model and finds the closest corresponding sampling point on theCurrent Teeth Image. A grid is created on each tooth and the number ofsamples is randomly selected and then the grid is overlaid on theCurrent Teeth Image.

In step 614, any resulting errors from the surface matching algorithmare compared to predetermined tolerances to determine if the resultingerrors are less than the predetermined tolerance. Error tolerances canaccount for potential differences in the models being compared thatmight impair meaningful comparison, such as errors due to typicalvariance between different scans or impressions, surface differences orfluctuations, and the like. If the resulting errors are greater than thepre-determined tolerance, then in step 616, error statistics for thesurface matching algorithm are typically output to a display device andcan be further redirected to a technician for manual input or correctionas in step 610.

If the resulting errors are less than the pre-determined tolerance, instep 618, then matching and comparison of the Previously Segmented TeethModel and the Current Teeth Image proceeds for a determination whetherthe actual arrangement of the patient's teeth deviates from the plannedarrangement. In particular, a determination can be made as to whetherpositional differences exist, and to what degree, between the teeth intheir current positions compared to the expected or planned positions.Positional differences may indicate whether the patient's teeth areprogressing according to the treatment plan or if the patient's teethare substantially off track. Various clinical and/or positionalparameters can be examined and compared for a determination as towhether a patient's teeth are substantially on track or are deviatingfrom an expected arrangement according to the treatment plan. Forexample, positional parameters examined can include tooth rotation,extrusion, intrusion, angulation, inclination, translation, and thelike. Threshold values for differences in one or more positionalparameters can be selected as being indicative of a significant orsubstantial difference in tooth position. Exemplary threshold values forvarious positional parameters, according to one embodiment of theinvention are listed in Table 1 below. Detecting positional differencesabove the selected threshold value(s) indicates that the actualarrangement of the patients teeth substantially deviates from theplanned arrangement to which the comparison is made.

TABLE 1 OFF TRACK PARAMETERS. The threshold difference values of aplanned position of teeth to actual positions selected as indicatingthat a patient's teeth have progressed substantially off-track.Difference Type Movement Actual/Planned Rotations Upper central incisors9 deg Upper lateral incisors 11 deg Lower incisors 11 deg Upper cuspids11 deg Lower cuspids 9.25 deg Upper Bicuspids 7.25 deg Lower FirstBicuspid 7.25 deg Lower Second Bicuspid 7.25 deg molars 6 deg ExtrusionAnterior 0.75 mm Posterior 0.75 mm Intrusion Anterior 0.75 mm Posterior0.75 mm Angulation Anterior 5.5 deg Posterior 3.7 deg InclinationAnterior 5.5 deg Posterior 3.7 deg Translation BL Anterior 0.7 mm BLPosterior Cuspids 0.9 mm MD Anterior 0.45 mm MD Cuspids 0.45 mm MDPosterior 0.5 mm

If the patient's teeth are determined to be on track by comparison ofthe teeth in their current positions with teeth in their expected orplanned positions, then treatment can progress according to the existingor original treatment plan (Step 620). For example, a patient determinedto be progressing on track can be administered one or more subsequentappliances according to the treatment plan, such as the next set ofappliances. Treatment can progress to the final stages and/or can reacha point in the treatment plan where bite matching is repeated for adetermination of whether the patient's teeth are progressing as plannedor if the teeth are off track. If the patient's teeth are determined offtrack and deviating from the planned arrangement, then treatmentaccording to the original treatment plan will be suspended. Typically, amodified or revised treatment plan will be generated where a patient'steeth are determined as being substantially off track (Step 622).Regardless of whether the patient's teeth are determined to be off trackor progressing according to the treatment plan, the process can generatea report or analysis of the results, and/or visualize the comparison,including any detected discrepancy (Step 624). Any such product can betransmitted, for example, to a technician or treating professional, tothe patient, or elsewhere.

FIG. 7 is a screen shot showing a graphical representation of athree-dimensional model of a patient's upper and lower jaws 640, 650generated from a Current Teeth Image. As described above, using adigital detailing tool (DDT), a technician pre-processes the CurrentTeeth Image by assigning and placing FACC's or unique currentidentifiers 74 on each tooth in the model. Unique current identifiersare landmarks on the teeth for the purposes of matching. Each FACC has anumber associated with it and that is the tooth number, so the sametooth from the Previously Segmented Teeth Models and the Current TeethImage should be in a similar location.

FIG. 8 is a graphical representation of a three-dimensional model of astarting match that can occur when a Previously Segmented Teeth Model isoverlaid on the Current Teeth Image, according to one embodiment of thepresent disclosure. The initial match provides a starting position forsubsequent surface matching so that a good match is achieved.

If the initial matching algorithm determines that one or more teeth aremismatched, the initial matching algorithm cannot complete the initialmatching satisfactorily because of teeth numbering irregularities ormissing FACCs. In this instance, the initial matching algorithm willgenerate an informational dialog giving details of the mismatchesallowing the technician to correct them and execute the initial matchingalgorithm again. Also shown in FIG. 8 are four attachments 660, 662,664, 666 that have been optionally added to four of the patient's teeth.

See also, e.g., U.S. Pat. No. 8,075,306, entitled “System and Method forDetecting Deviations During the Course of an Orthodontic Treatment toGradually Reposition Teeth,” issued Dec. 13, 2011, the full disclosureof which is incorporated herein by reference, for further discussion ofcomparing an unsegmented representation of an actual arrangement of apatients teeth after treatment has begun, to a previously segmentedmodel of the patient's teeth.

While the timing of the progress tracking steps described herein can beselected by the practitioner, typically at least general timing forconducting progress tracking measures of the present invention will beincorporated into the treatment plan and, therefore, will be pre-plannedor planned at about the beginning of treatment or early on in the courseof the patient's treatment (e.g., prior to the patient wearing a givenset of appliances so as to reposition the teeth). Thus, in oneembodiment of the invention, a treatment plan will include a prescribedtiming for the planned tracking steps. The prescribed timing can includea specifically recommended date or may include a general increment oftime (e.g., at treatment week 9, 10, 11, etc.), or can be based on thetiming of other events of the treatment plan (e.g., after a patientwears a set of appliances).

Timing of progress tracking steps can be selected to occur based on asomewhat standardized treatment protocol or can be more particularlycustomized to an individual patient. More standardized protocols cantake into account certain population statistics, generalized clinicalexpectations, and/or physiological parameters that can be used togenerally predict rate of movement of a patient's teeth and the minimumlength of treatment time necessary for the patient's teeth to progressoff track if such progression is occurring. Clinical parameters caninclude, for example, root structure, including length, shape, andpositioning, as well as certain jaw characteristics such as jaw bonedensity, patient age, gender, ethnicity, medications/health historyprofile, dental history including prior treatment with orthodontics,type of orthodontic treatment plan (extraction vs. non-extraction), andthe like. Assuming a 2-week wear interval for each appliance, with amaximum tooth velocity of 0.25 mm/tooth per aligner, typically about 16to 20 weeks of repositioning treatment (8 to 10 appliances) is requiredbefore movement of the teeth is substantial enough to detect anoncompliant or off track movement of the teeth, if such off trackmovement is occurring, though more drastic movements can produce offtrack movement after only a few weeks.

As set forth above, timing of tracking measures can be selected based onthe particular movement(s) prescribed and/or characteristics of thepatient being treated and, therefore, are said to be customized to theparticular patient. For example, certain desired tooth movements in atreatment plan may be deemed either more unpredictable or at increasedrisk of moving off track and may require specifically timed tracking ormonitoring. For example, for certain movements including, e.g.,extrusions or rotations of round teeth (e.g., canines), more specific orfrequent tracking may be desired. Additionally, certain physiological orclinical characteristics of the patient may be identified as indicatingthat particularly timed and/or frequency of tracking might be desired.Whether tracking is selected based on standardized protocols or morecustomized to the individual patient, tracking may or may not beselected to uniformly timed during the course of treatment. For example,a lower frequency of tracking measures may be desired or needed duringcertain portions or phases of treatment than others (e.g., spaceclosure). Regardless of whether tracking timing is customized or morestandardized, the selected timing will typically provide the additionaladvantage of efficiently planning tracking in the treatment plan tominimize unnecessary use of practitioner time and other resources.

Once a determination is made that the patient's actual arrangement ofteeth deviates from a planned arrangement and that the patient's teethare not progressing as expected/planned, a change or correction in thecourse of treatment can be selected, for example, by generating arevised or modified treatment plan. Referring to FIGS. 9A-9C, revisedtreatment following determination that a patient's teeth are notprogressing on track is described. As set forth above, a treatment planincludes a plurality of planned successive tooth arrangements for movingteeth along a treatment path from an initial arrangement to a selectedfinal arrangement. The treatment plan, administration of sets ofappliances to a patient according to the planned arrangements, caninclude a plurality of phases (1 through 4) where at time=0, the initialtreatment plan begins. The initial treatment plan is illustrated by asolid line. Bite matching for a determination of whether a case isprogressing “on track” or “off track”, as described above (e.g., FIGS.5, 6), can take place at one or more of the phases or points along theadministration of treatment.

In particular, current tooth positions of the patient can be obtainedfrom the patient any one or more phases and compared to segmented modelsof the patient's teeth according to an earlier or original treatmentplan. Where teeth are determined to be deviating from the plannedtreatment plan or progressing “off track”, as illustrated by brokenlines, modification or revision of treatment plan can occur. In oneembodiment, a revised treatment plan can include restaging the patient'streatment from the determined actual position to the originallydetermined final position (FIG. 9A). Revised treatment path (illustratedby dashed lines) can proceed directly toward the initially determinedfinal position and need not attempt to redirect treatment back onto theoriginal treatment path. In this case, while partialoverlap/intersection of the revised treatment path with the originaltreatment path may occur, the revised treatment path will at leastpartially diverge from the initial treatment path and proceed directlytoward the initially determined final arrangement of the teeth. Such anapproach may be selected, for example, where retaining the initiallydetermined final position is desired. This approach also advantageouslypermits use of the originally processed and segmented data, therebyallowing avoidance of costly processing steps.

Alternatively, a revised treatment plan can include a more direct“mid-course correction”, in which the revised treatment plan includes amore direct path back toward the a planned arrangement of the initialtreatment plan, as illustrated in FIG. 9B. While this approach may makeuse of the originally planned final arrangement, the more primaryconcern in this example type of correction is redirecting treatment backto the original treatment path, rather than from the actual position andmore directly toward the original final position. In yet anotherembodiment, as illustrated in FIG. 9C, a revised treatment plan caninclude essentially “restarting” treatment, and generating a new finalarrangement of the teeth, for example, from segmenting and staging a newimpression of the teeth, and directing the patient's teeth from theactual arrangement to the newly determined final arrangement of theteeth.

FIG. 10 is a simplified block diagram of a data processing system 700that may be used in executing methods and processes described herein.The data processing system 700 typically includes at least one processor702 that communicates with a number of peripheral devices via bussubsystem 704. These peripheral devices typically include a storagesubsystem 706 (memory subsystem 708 and file storage subsystem 714), aset of user interface input and output devices 718, and an interface tooutside networks 716, including the public switched telephone network.This interface is shown schematically as “Modems and Network Interface”block 716, and is coupled to corresponding interface devices in otherdata processing systems via communication network interface 724. Dataprocessing system 700 can include, for example, one or more computers,such as a personal computer, workstation, mainframe, and the like.

The user interface input devices 718 are not limited to any particulardevice, and can typically include, for example, a keyboard, pointingdevice, mouse, scanner, interactive displays, etc. Similarly, varioususer interface output devices can be employed in a system of theinvention, and can include, for example, one or more of a printer,display (e.g., visual, non-visual) system/subsystem, controller,projection device, audio output, and the like.

Storage subsystem 706 maintains the basic required programming,including computer readable media having instructions (e.g., operatinginstructions, etc.), and data constructs. The program modules discussedherein are typically stored in storage subsystem 706. Storage subsystem706 typically comprises memory subsystem 708 and file storage subsystem714. Memory subsystem 708 typically includes a number of memories (e.g.,RAM 710, ROM 712, etc.) including computer readable memory for storageof fixed instructions, instructions and data during program execution,basic input/output system, etc. File storage subsystem 714 providespersistent (non-volatile) storage for program and data files, and caninclude one or more removable or fixed drives or media, hard disk,floppy disk, CD-ROM, DVD, optical drives, and the like. One or more ofthe storage systems, drives, etc may be located at a remote location,such coupled via a server on a network or via the Internet's World WideWeb. In this context, the term “bus subsystem” is used generically so asto include any mechanism for letting the various components andsubsystems communicate with each other as intended and can include avariety of suitable components/systems that would be known or recognizedas suitable for use therein. It will be recognized that variouscomponents of the system can be, but need not necessarily be at the samephysical location, but could be connected via various local-area orwide-area network media, transmission systems, etc.

Scanner 720 includes any means for obtaining an image of a patient'steeth (e.g., from casts 721), some of which have been described hereinabove, which can be obtained either from the patient or from treatingprofessional, such as an orthodontist, and includes means of providingthe image data/information to data processing system 700 for furtherprocessing. In some embodiments, scanner 720 may be located at alocation remote with respect to other components of the system and cancommunicate image data and/or information to data processing system 700,for example, via a network interface 724. Fabrication system 722fabricates dental appliances 723 based on a treatment plan, includingdata set information received from data processing system 700.Fabrication machine 722 can, for example, be located at a remotelocation and receive data set information from data processing system700 via network interface 724.

It is understood that the examples and embodiments described herein arefor illustrative purposes and that various modifications or changes inlight thereof will be suggested to persons skilled in the art and are tobe included within the spirit and purview of this application and thescope of the appended claims. Numerous different combinations arepossible, and such combinations are considered to be part of the presentinvention.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

What is claimed is:
 1. A method for identifying and correctingdeviations of a patient's teeth from an orthodontic treatment plan, themethod comprising: comparing, using one or more processors, a previouslysegmented three-dimensional (3D) digital model of a target tootharrangement specified by the orthodontic treatment plan to anunsegmented 3D digital model of a current tooth arrangement of thepatient; identifying, using one or more processors, a discrepancybetween the current tooth arrangement and the target tooth arrangementbased on the comparing; and generating, using one or more processors, amodified orthodontic treatment plan in response to the identifieddiscrepancy.
 2. The method of claim 1, wherein the comparing stepcomprises matching a surface of at least one tooth from the previouslysegmented 3D digital model to a surface of at least one correspondingtooth from the unsegmented 3D digital model.
 3. The method of claim 1,wherein the comparing step comprises calculating at least one positionaldifference between at least one tooth of the current tooth arrangementand at least one corresponding tooth of the target tooth arrangement. 4.The method of claim 3, wherein the identifying step comprisesdetermining that the at least one positional difference exceeds apredetermined threshold value.
 5. The method of claim 1, wherein theorthodontic treatment plan comprises moving the patient's teeth along aninitial treatment path from an initial tooth arrangement towards asubsequent tooth arrangement, and the modified orthodontic treatmentplan comprises moving the patient's teeth along a revised treatment pathfrom the current tooth arrangement directly towards the subsequent tootharrangement.
 6. The method of claim 1, wherein the orthodontic treatmentplan comprises moving the patient's teeth along an initial treatmentpath from an initial tooth arrangement towards a subsequent tootharrangement, and the modified orthodontic treatment plan comprisesmoving the patient's teeth from the current tooth arrangement towards atooth arrangement specified by the initial treatment path.
 7. The methodof claim 1, wherein the orthodontic treatment plan comprises moving thepatient's teeth along an initial treatment path from an initial tootharrangement towards a first subsequent tooth arrangement, and themodified orthodontic treatment plan comprises moving the patient's teethalong a revised treatment path from the current tooth arrangementtowards a second subsequent arrangement different from the firstsubsequent tooth arrangement.
 8. The method of claim 1, furthercomprising generating, using one or more processors, instructions forfabricating at least one orthodontic appliance shaped to reposition thepatient's teeth in accordance with the modified orthodontic treatmentplan.
 9. A system for identifying and correcting deviations of apatient's teeth from an orthodontic treatment plan, the systemcomprising: one or more processors; and memory, including instructionsexecutable by the one or more processors to cause the system to atleast: compare a previously segmented three-dimensional (3D) digitalmodel of a target tooth arrangement specified by the orthodontictreatment plan to an unsegmented 3D digital model of a current tootharrangement of the patient, identify a discrepancy between the currenttooth arrangement and the target tooth arrangement based on thecomparing, and generate a modified orthodontic treatment plan inresponse to the identified discrepancy.
 10. The system of claim 9,wherein the orthodontic treatment plan comprises moving the patient'steeth along an initial treatment path from an initial tooth arrangementtowards a subsequent tooth arrangement, and the modified orthodontictreatment plan comprises moving the patient's teeth along a revisedtreatment path from the current tooth arrangement directly towards thesubsequent tooth arrangement.
 11. The system of claim 9, wherein theorthodontic treatment plan comprises moving the patient's teeth along aninitial treatment path from an initial tooth arrangement towards asubsequent tooth arrangement, and the modified orthodontic treatmentplan comprises moving the patient's teeth from the current tootharrangement towards a tooth arrangement specified by the initialtreatment path.
 12. The system of claim 9, wherein the orthodontictreatment plan comprises moving the patient's teeth along an initialtreatment path from an initial tooth arrangement towards a firstsubsequent tooth arrangement, and the modified orthodontic treatmentplan comprises moving the patient's teeth along a revised treatment pathfrom the current tooth arrangement towards a second subsequentarrangement different from the first subsequent tooth arrangement. 13.The system of claim 9, further comprising a user interface configured toreceive user input indicating locations of at least one landmark on eachtooth of the unsegmented 3D digital model.
 14. The system of claim 13,wherein the at least one landmark comprises a facial axis of theclinical crown (FACC) identifier.
 15. The system of claim 13, whereinthe compare step comprises matching the at least one landmark on eachtooth of the unsegmented 3D digital model to at least one correspondinglandmark on each tooth of the previously segmented 3D digital model. 16.The system of claim 9, further comprising a user interface configured todisplay a visualization of the discrepancy between the current tootharrangement and the target tooth arrangement to a user.
 17. One or morenon-transitory computer-readable storage media having stored thereonexecutable instructions that, when executed by one or more processors ofa computer system for identifying and correcting deviations of apatient's teeth from an orthodontic treatment plan, cause the computersystem to at least: compare a previously segmented three-dimensional(3D) digital model of a target tooth arrangement specified by theorthodontic treatment plan to an unsegmented 3D digital model of acurrent tooth arrangement of the patient, identify a discrepancy betweenthe current tooth arrangement and the target tooth arrangement based onthe comparing, and generate a modified orthodontic treatment plan inresponse to the identified discrepancy.
 18. The one or morenon-transitory computer-readable storage media of claim 17, wherein theorthodontic treatment plan comprises moving the patient's teeth along aninitial treatment path from an initial tooth arrangement towards asubsequent tooth arrangement, and the modified orthodontic treatmentplan comprises moving the patient's teeth along a revised treatment pathfrom the current tooth arrangement directly towards the subsequent tootharrangement.
 19. The one or more non-transitory computer-readablestorage media of claim 17, wherein the orthodontic treatment plancomprises moving the patient's teeth along an initial treatment pathfrom an initial tooth arrangement towards a subsequent tootharrangement, and the modified orthodontic treatment plan comprisesmoving the patient's teeth from the current tooth arrangement towards atooth arrangement specified by the initial treatment path.
 20. The oneor more non-transitory computer-readable storage media of claim 17,wherein the orthodontic treatment plan comprises moving the patient'steeth along an initial treatment path from an initial tooth arrangementtowards a first subsequent tooth arrangement, and the modifiedorthodontic treatment plan comprises moving the patient's teeth along arevised treatment path from the current tooth arrangement towards asecond subsequent arrangement different from the first subsequent tootharrangement.